I've got a 91 Nissan Primera and recently there has been a really weird whistling type noise coming from the front left wheel. It usually starts doing that after iv'e driven for about 5 minutes and it does it when I am cruising at about 50-60 km/h. The noise does go away when I apply the brakes at like a traffic light or something and when I pull away and get up to 50-60 it starts up again. Lately it's been getting more frequent and at times even louder. I just had new brake pads fitted yesterday, but the problem is still there and at some points the whistling squeeling type noise is worse. The noise is greatly reduced and sometimes not even there when I am driving in the rain.

I'm gonna guess that there's a problem with the wheel bearing. You probably want to get it into a shop (unless you're particularly mechanically inclined) and have them check it over. Have you noticed any weird tire wear on that side i.e. cupping, unequal wear, etc?